Commonly assigned, U.S. Pat. Nos. 5,388,594, 5,505,214, and 5,591,368 disclose various electrically operated lighters and cigarettes which cooperate to significantly reduce sidestream smoke while permitting the smoker to selectively suspend and reinitiate smoking. U.S. Ser. No. 08/380,718 was preceded by a commonly assigned patent application which issued as U.S. Pat. No. 5,388,594 (PM 1697).
The preferred embodiment of the lighter in U.S. Pat. No. 5,388,594 includes a plurality of metallic serpentine heaters disposed in a configuration that slidingly receives a tobacco rod portion of the system's cigarette. The cigarette and the lighter are configured such that when the cigarette is inserted into the lighter and as individual heaters are activated for each puff, localized charring occurs at spots about the cigarette in the locality where each heater bears against the cigarette (hereinafter referred to as a "heater footprint").
In U.S. Pat. No. 5,388,594, the sequence and the amount of energy applied to each heater element during a puff cycle is regulated by a logic circuit of a controller which executes a power subroutine upon its receiving a signal from a puff sensor that a puff has been initiated. The power subroutine includes the steps of reading the voltage of the power source (batteries) at the initiation of the puff and resolving a shut-off signal to a constant Joules energy timer such that the duration of the pulse (its cycle-period) is adjusted relative to the voltage of the power source to provide the same total amount of energy (Joules) throughout the range of voltages of the battery discharge cycle. It has been discovered that this sort of power subroutine may provide the smoker a different tasting smoking experience at the extremes of the battery discharge cycle. At full battery voltage, this type of control circuit would heat a cigarette more intensively for a shorter pulse duration than a cigarette smoked near or at the conclusion of the battery discharge cycle, where the cigarette would be heated at lower power for a longer period of time (pulse cycle).
Accordingly, a need has been perceived for a controller in an electrically operated cigarette lighter which duplicates the thermal treatment of a cigarette throughout the discharge cycle of its batteries/power source.
In commonly assigned U.S. Pat. No. 5,372,148 to McCafferty et al, a controller for an electrical smoking system is disclosed having a power subroutine that includes the steps of reading battery voltage and setting an estimated pulse duration length (e.g. 1 second) and dividing the cycle into a number of intervals (e.g. 10 intervals, each 100 milli-seconds), wherein the amount of energy required to generate aerosol is proportioned among the intervals in substantially equal factional amounts. During execution of the cycle, the controller monitors the amount of energy supplied to the selected heater element during each power interval and continues application of power until the correct proportional amount of energy has been delivered during the interval.
Because the power scheme of U.S. Pat. No. 5,372,148 changes cycle duration responsively to battery voltage, the power subroutine will change the thermal treatment of the cigarette as the batteries proceed through their discharge voltage cycles.
In U.S. Pat. No. 4,947,874 to Brooks et al, a smoking article includes a singular electrical resistance heating element that is impregnated with aerosol forming material and which is heated in a succession of power cycles. The article includes a current regulating circuit which provides an uninterrupted current flow immediately upon draw for about 1.5 to about 2 seconds followed by an "off" period of about 0.5 to about 1 second. The patent also proposes an alternative to an on-off time-based circuit, which alterative would include on-off and current modulating means connected to temperature sensors or other sensors that would sense either the temperature of the heating element directly or the temperature of air passing the heating element or the temperature of a second resistor having a character related to that of the aerosol carrying heating element.
The article disclosed in U.S. Pat. No. 4,947,874 is disadvantaged by its repetitively heating a singular heater and the material impregnated thereon, which creates a situation of already depleted tobacco material being heated again and again. Additionally, targeting temperature at different battery voltages may affect the rate at which energy is supplied to the heater, which in turn could affect how the article thermally treats the aerosol forming material.